Middle East respiratory syndrome coronavirus
Sympathetic Nervous System
inflammatory bowel disease
severe acute respiratory syndrome
January 17, 2016
Dr. Matthew Gray
Any dog owner can attest to the fact dogs are messy drinkers. After a dog has
had its fill, there is usually water all over the floor (and all over their face). But
why is this? It has long been assumed that dogs drink in a similar fashion to cats,
which has been studied before , but cats don't make such a mess when drinking.
To determine how dogs drink differently from cats, Gart et al.  approached the
problem from a fluid dynamics perspective, using both video capture of dogs
drinking and physical experiments employing artificial analogues that simulate
dogs drinking to determine how the water moves during a dogs drinking action.
It had been believed that dogs drink by scooping water into their mouths with a
"ladle" they form by curling their tongue backwards. However, this view was
refuted, and Gart et al. worked to study how dogs drink if they don't scoop the
water this way. They observed that the dogs pushed their tongue just below
surface of the water, then accelerated it upwards, drawing a column of water
upwards through contact with the convex bottom side of the tongue "ladle". The
dogs would snap their jaws shut just as the water column was about the separate
from the tongue, thus maximizing the amount of water within their mouth. The
researchers created a scalable model of a dog drinking whereby round bottomed
glass rods, attached to extended springs that would recoil when the rod was
released were used in place of a dog's tongue. Using this setup with rods of
different diameters to mimic different sized dogs, the researchers were able derive
an equation to predict when a dog of a certain size would close their jaws to
capture the water. Upon comparison to videos of various dog breeds of different
sizes all drinking water, they concluded that their equation correctly predicted
when the dogs captured the water, indicating they had successfully determined the
physics behind how dogs drink.
Through their work, Gart et al. showed that dogs do not scoop water to drink,
but rather draw up water and capture it in much the same way cats do. But why the
mess with dogs and not cats? The authors suggest that this may be due to the dogs
inserting their tongue below the water's surface, unlike cats who just contact the
surface, allowing water to be captured by the "ladle". This water is not drunk, but
rather may be flung from the tongue as it accelerates during retraction into the
mouth. So, more work needs to be done to determine the physics behind why you
have to clean up after your dog when they refresh themselves!
Cover photo: Screen capture from the video "Secret Life of Dogs" by Oxford Scientific Films 2013.
 Reis, PM, Jung, S, Aristoff, JM, and Stocker, R. How cats lap: water uptake by
Felis catus. Science, 2010. 330 (6008): 1231-1234.
 Gart, S, Socha, JJ, Vlachos, PP, and Jung, S. Dogs lap using acceleration-
driven open pumping. PNAS USA, 2015. 112 (52): 15798-15802.